Which of the following must personnel check before using hand-held instruments?

Before using hand-held instruments, personnel must ensure that several critical checks are performed to ensure safety and accuracy in measurements.

Ensuring the instrument is in service means that it has been properly maintained and is functioning correctly. Regular maintenance can prevent malfuncitons that may lead to inaccurate readings.

Checking that the audio output can be heard is also important, especially for dosimeters or radiation alert systems that may provide audio warnings when certain radiation levels are exceeded. If the audio output is not functioning, operators could miss critical alerts regarding hazardous levels of radiation.

Setting the instrument to the proper scale is crucial as it directly affects the accuracy of the measurements taken. If the instrument is not set to the correct range for the expected radiation levels, readings could be misinterpreted, leading to incorrect assessments of exposure or contamination.

Collectively, these checks are essential for the safe and effective use of hand-held instruments, making it clear that all these factors must be verified before operation.